The invention relates to a process for the preparation of 4,5,6-trichloro- and 2,4,5,6-tetrachloropyrimidine starting from 3-dimethylaminopropionitrile, to its use and also to a crystalline intermediate product form.
According to US-A 3 509 032, 4,5,6-trichloro- and 2,4,5,6-tetrachloropyrimidine are obtained by chlorination of 3-dimethylaminopropionitrile with Cl2 with irradiation by UV light, it being necessary for the temperature of the chlorination to sometimes be above 150xc2x0 C., in particular from 180 to 220xc2x0 C., in order to permit the desired products to form (see column 2, line 51 to 53 and Example 2 and 3). Such high chlorination temperatures are, however, disadvantageous when carrying out the procedure industrially.
According to DE-A 3 900 917, 4,5,6-trichloropyrimidine is prepared from the hydrochloride of 3-dimethylaminopropionitrile in a single-step chlorination at a temperature of from 120 to 130xc2x0 C. However, some aspects of this procedure can still be improved upon, in particular as regards its suitability for large-scale batches.
Furthermore, most of the processes described in the prior art have the disadvantage that during subsequent distillation insoluble distillation residues are formed, which can only be removed from the distillation vessels at considerable expense. In addition, the resulting products gas very severely during distillation.
The object of the present invention was therefore to provide a process for the preparation of 4,5,6-trichloro- and 2,4,5,6-tetrachloropyrimidines starting from 3-dimethethylaminopropionitrile which does not have the above disadvantages.
We have found a process for the preparation of 4,5,6-trichloro- and 2,4,5,6-tetrachloropyrimidine by reacting 3-dimethylaminopropionitrile with HCl and Cl2, which comprises
a) in a first reaction step reacting 3-dimethylaminopropionitrile in a solvent, preferably one inert towards HCl and Cl2, with HCl, preferably from 1 to 6 mol, and Cl2, preferably from 2 to 4 mol, in each case based on 1 mol of 3-dimethylaminopropionitrile, at a temperature of from xe2x88x9210 to 55xc2x0 C., and
b) in a second reaction step reacting the reaction mixture from the first reaction step with Cl2, preferably from 3 to 5 mol, based on 1 mol of 3-dimethylaminopropionitrile used, at a temperature above 55xc2x0 C., preferably from 65 to 120xc2x0 C., optionally in the presence of a catalyst,
characterized in that the second reaction step is carried out in the presence of the reaction product from the first reaction step, which is in microcrystalline form with an average crystal size of xe2x89xa610 xcexcm.
The solvents which are inert towards HCl and Cl2 under reaction conditions are preferably taken to mean those which are inert under the specified reaction conditions of the process according to the invention. Examples of suitable solvents are chlorinated, aliphatic and aromatic hydrocarbons, such as chloroform, tetrachloromethane, chlorobenzene, dichlorobenzene, isododecane, phosphorus oxychloride or mixtures thereof. Particular preference is given to phosphorus oxychloride (POCl3).
The first reaction step of the process according to the invention is preferably carried out at a temperature of from 15 to 25xc2x0 C. It can, for example, be carried out batchwise or continuously.
The batchwise process variant involves, for example, initially introducing the 3-dimethylaminopropionitrile, preferably in the solvent inert towards Cl2 and HCl, and passing HCl into it. The amount of HCl to be introduced is generally from 1 to 6 mol, preferably from 3 to 4 mol, based on 1 mol of the 3-dimethylaminopropionitrile used. The resulting HCl adduct of the nitrile is particularly readily soluble in the temperature range according to the invention when the solvent used is phosphorus oxychloride. The heat produced during HCl introduction with HCl adduct formation is preferably dissipated by cooling. This is then followed by the reaction with preferably from 2 to 4 mol of Cl2 per mole of 3-dimethylaminopropionitrile. To this end, Cl2 is passed into the reaction mixture for the HCl reaction with evolution of HCl. The introduction is preferably carried out at from 15 to 20xc2x0 C.
The above-described batchwise variant preferably involves introducing from 1 to 2 mol of HCl before starting to introduce Cl2. The HCl adduct formation of the nitrile is then completed by the HCl formed during the chlorination.
The batchwise process variant is preferably chosen for small batches, in particular for batches smaller than 10 mol, based on 3-dimethylaminopropionitrile.
Particular preference is given to carrying out the reaction of the first reaction step of the process according to the invention continuously. In the continuous method, the solvent inert towards Cl2 and HCl, in particular phosphorus oxychloride, 3-dimethylaminopropionitrile, HCl and Cl2 are preferably brought together continuously in a reactor. The amount of HCl is preferably from 1 to 2 mol per mole of 3-dimethylaminopropionitrile.
The amount of Cl2 corresponds to that mentioned at the outset. The HCl formed during the chlorination preferably remains in the reaction mixture and thus does not need to be fed in from outside. The heat which is liberated during the reaction is preferably dissipated by cooling. The temperature for the continuous method is particularly preferably maintained at from 15 to 25xc2x0 C.
The reaction in the 1st reaction step is particularly preferably carried out completely continuously, this being taken to mean the continuous introduction of reactants and the continuous removal of reaction product.
If phosphorus oxychloride is used as preferred solvent, the reaction mixture in the first reaction step which is formed continuously is in the form of a solution at a temperature of from xe2x88x9210 to +55xc2x0 C.
The reaction products formed in the first reaction step of the process according to the invention are preferably the hydrochlorides of the chlorinated 3-dimethylaminopropionitrile, which preferably conform to the formulae (I) and (II) 
in which
x is a number from 1 to 3, preferably 3.
With particular preference, a product mixture is formed in which the compounds of the formulae (I) and (II) are present in a ratio of from 10:1 to 2:1.
The amount of solvent used can be varied over wide ranges. It is preferable to use from 4 to 10 parts of solvent per part of 3-dimethylaminopropionitrile used.
In a particularly preferred embodiment of the process according to the invention, the reaction mixture from the first reaction step and further Cl2 are brought together semi-continuously at the temperature of the second reaction step, i.e. such that the bringing together, preferably in a second reactor, takes place for as long as the size of this reactor permits filling. In this connection, any catalyst which is used can, for example, be introduced with the introduced reaction mixture of the first reaction step or, for example, already be present in the reactor.
In the second reaction step HCl is formed. It is formed on the one hand during the chlorination and is, on the other hand, liberated from the HCl adduct of the first reaction step to form a monohydrochloride.
Transferring the reaction mixture of the first reaction step to the second step, preferably to the second reactor, results in crystalline precipitation. Furthermore, transfer to the second reaction step, which proceeds at a higher temperature (compared with the first reaction step) leads to the evolution of HCl. When the reaction mixture is transferred to the 2nd reaction step, coarse crystalline precipitations initially form. After a short time, finer crystals (microcrystals) can then be observed.
Both the coarse and also the fine crystals are crystals or mixed crystals of monohydrochlorides of the formulae (Ia) and/or (IIa). 
These initially precipitate as relatively coarse crystals which have an average crystal size of  greater than 10 xcexcm. These coarse crystals preferably precipitate in the form of colourless platelets which are cuboid and have an edge length of from 0.05 to 0.2 mm and a thickness of about 0.01 mm. These crystals preferably comprise the compounds Ia and IIa in a weight ratio of from 10:1 to 2:1.
The invention also relates to crystals with an average crystal size of xe2x89xa610 xcexcm comprising the compounds of the formula Ia and/or IIa. 
These preferably comprise the compounds of the formulae Ia and IIa in a weight ratio of from 10:1 to 2:1.
The microcrystals are preferably in the form of needles or rods which have a length of from 2 to 6 xcexcm and a thickness of from 0.5 to 1 xcexcm.
The invention further relates to a process for the preparation of these microcrystals, which is characterized in that 3-dimethylaminopropionitrile in a solvent which is inert towards HCl and Cl2 is reacted with from 1 to 6 mol of HCl and from 2 to 4 mol of Cl2, in each case based on 1 mol of 3-dimethylaminopropionitrile, at a temperature of from xe2x88x9210 to 55xc2x0 C., and then the resulting reaction mixture is heat-treated at a temperature of from 65 to 85xc2x0 C.
In a particularly preferred embodiment of the process according to the invention for the preparation of the chloropyrimidines, the ratio of microcrystals to a coarse crystalline form is from 95:5 to 50:50.
The process according to the invention is particularly suitable for batches  greater than 1 kmol, based on 3-dimethylaminopropionitrile.
The second reaction step preferably follows the 1st reaction step immediately, so that the residence time between the two steps is kept as short as possible.
If the finely crystalline monohydrochloride is isolated, it can be used as seed crystals for the second reaction step. In this case, the same advantageous effect is achieved, even without awaiting the formation of fine crystalline precipitation.
The reaction product of the 1st reaction step is preferably transferred to the second reactor such that the fraction of the microcrystals, which only form slowly, relative to the coarse crystalline form does not become too small since it has been found that the coarse crystalline form is unstable under the reaction conditions. The ratio of microcrystals to the coarse crystalline form is preferably from 95:5 to 50:50.
In a very particularly preferred embodiment of the second reaction step, the reaction is carried out in the presence of a catalyst. Possible catalysts which may be mentioned are, for example, organic catalysts. Suitable organic catalysts are, for example, open-chain or cyclic carboxamides, such as C1-C12-dialkylformamides, in particular dimethylformamide, dibutylformamide, methyldodecylformamide, Nxe2x80x94C1-C12-alkylpyrrolidones, such as N-methyl-2-pyrrolidone, Nxe2x80x94C1-C12-alkylcaprolactams, such as N-methylcaprolactam, and also trialkyl phosphites, triaryl phosphites, triarylphosphine oxides, where aryl is preferably optionally substituted phenyl. Particular preference is given to triphenylphosphine oxide.
The catalysts can also be used in a mixture with one another, preferably in amounts of from 1 to 10% by weight, preferably from 2 to 5% by weight, based on 3-dimethylaminoproplonitrile used.
The second reaction step of the process according to the invention is very particularly preferably carried out in the presence of free-radical scavengers. Preference is given to oxygen, in particular in the form of air. Air is, for example, preferably introduced into the reaction mixture in an amount of from 10 to 100 l per 1 kg of 3-dimethylaminopropionitrile used, in particular continuously throughout the reaction period.
Very particular preference is given to the process according to the invention in which the HCl formed in the second reaction step, optionally together with excess Cl2 from the second reaction step, is returned to the first reaction step, as a result of which it is not necessary to introduce more HCl from outside. The process according to the invention in a particularly preferred embodiment is thus autarkic with respect to HCl.
The process according to the invention preferably produces 4,5,6-trichloro- and 2,4,5,6-tetrachloropyrimidine as a mixture. The composition in favour of one of the two pyrimidines can preferably be controlled via the temperature. In this connection, the trichloropyrimidine, for example, for the same reaction time, is preferably formed at a reaction temperature of from 85 to 105xc2x0 C., whilst the 2,4,5,6-tetrachloropyrimidine is preferably formed at a temperature of from 65 to 75xc2x0 C. Chloropyrimidine mixtures obtained in this way preferably have a ratio of trichloro- to tetrachloropyrimidine of from 4:1 to 1:30.
The resulting 4,5,6-trichloro- and 2,4,5,6-tetrachloropyrimidine and the solvent used are preferably fractionally distilled for the purposes of isolation and recovery. After the respective product has been distilled off, it is possible to obtain in each case a second fraction of the product from the distillation residue in the presence of a little activated carbon. The relatively small amount of distillation residues which remain are readily soluble in, for example, o-dichlorobenzene, and can in this form, for example, be incinerated.
4,5,6-Trichloro- and 2,4,5,6-tetrachloropyrimidine are, for example, important intermediates for the preparation of fluorine-containing reactive components, such as those incorporated into reactive dyes (see DE-A 1 644 203), and are also suitable as intermediates for crop-protection compositions and pharmaceuticals.
The invention is further described in the following illustrative examples. All parts are by weight, unless otherwise noted.